I found the perfect colour of green yarn, and so, I have my Halloween costume. I made a brain slug!
I've seen a few patterns online, but ended up making it up as I went along. 2 strands held together in hdc made up like a kids hat (started with 14 on the first round & increased each round until it seemed wide enough. The last row I used a modified petal pattern. The eyeball is a yo-yo from an old t-shirt with a black button. I did a 4 stitch i-cord for the antenna, tied in a knot at the end.
All in all I'm pretty satisfied with it, and it will serve perfectly well for a work-place costume. (x-posted a few places, sorry for any repeats!)